A brand new Expedition will have 9200 lbs towing capacity and 1570 cargo capacity. And that's "properly equipped."
If that 8500 lbs is actual scale weight, you'd still be very close to max BEST case scenario. But you cargo capacity will likely be exceeded.
I'm assuming you desire an SUV for passengers since you mentioned 8 passenger capacity. Well, that many people will likely get you over the cargo capacity right there. Let alone their gear.
Also, SUV, Travel Trailer, and fuel economy just aren't words that should be together. It ain't gonna happen